1. Field of the Invention
The present invention relates to a gate valve and, more particularly, to improvements in which a pair of valve plates connected to each other with bellows are used to open and close a valve of a valve casing and the like, thereby reducing the differential-pressure generating force applied to a driving valve plate by valve-operation driving force, and allowing the valve plates and a valve-plate driving section to be lightweight and to have low rigidity.
2. Description of the Related Art
Conventionally, structures of non-sliding vacuum gate valves disclosed in, for example, Japanese Unexamined Patent Application Publication Nos. 8-42715 and 10-110834, which are not shown, are generally adopted.
In this constructed conventional non-sliding vacuum gate valves, the following problems occur:
Since a simple valve plate having no bellows is vertically moved to open and close a valve of an opening of a valve casing, if the relationship between the pressure P0 on the side of a valve plate 1 and the pressure P1 on the side of a valve casing 2 satisfies the condition P1 greater than P0, the pressure P1 is applied to an area Sa surrounded by a sealing member 3 so that the valve plate 1 separates from a valve seat 4 as in FIG. 1.
A force f, where f=(P1xe2x88x92P0)xc2x7Sa, is applied and it becomes necessary to add the value f to the seating force which is originally required in order to achieve the operating force required for the valve closing (sealing) operation. Therefore, the valve plate and the valve-plate driving section are required to have a large weight and high rigidity, and consequently, the structure of the gate valve itself becomes so large and complicated that it is difficult to manufacture at a low cost.
The present invention has been made to solve the above problems. Accordingly, it is an object of the present invention to provide a gate valve in which a pair of valve plates connected to each other with bellows are used to open and close a valve of a valve casing and the like, thereby reducing the differential pressure serving as resistance against a valve-operation driving force and allowing the valve plates and a valve-plate driving section to be lightweight and to have low rigidity.
A gate valve according to the present invention comprises: a first valve plate having a valve opening; and a second valve plate connected to the first valve plate via a first bellows. Preferably, the first valve plate has a valve rod connected thereto, a plurality of the first bellows are arranged in parallel, the first valve plate has valve openings, each corresponding to one of the first bellows, and the first valve plate has a first sealing member at a surface thereof. The gate valve according to the present invention further comprises: a valve casing for enclosing the valve plates in a manner so as to be moved; a first valve seat formed at a first opening of the valve casing and with which the first sealing member comes into contact; and a first stopper formed at a second opening of the valve casing and with which the second valve plate comes into contact. Preferably, the valve casing has a second stopper provided on the inside thereof, the second stopper being located between the first and second valve plates and coming into contact with the inner face of the second valve plate. A gate valve according to the present invention further comprises: a valve casing for enclosing the valve plates in a manner so as to be moved; a first sealing member formed at a first opening of the valve casing; and a first stopper formed at a second opening of the valve casing, with which the second valve plate comes into contact. Preferably, the first valve plate has a second stopper provided on the inside of the first bellows, the second stopper coming into contact with the second valve plate, and the second valve plate has a second stopper extending to the side of the first valve plate, which is provided on the inside of the first bellows. Preferably, the second valve plate has the second stopper extending to the side of the first valve plate and located on the outside of the first bellows. Preferably, a pressure-receiving area of the seat section of the first valve plate is smaller than a pressure-receiving area of the first bellows, which is based on the opening of the first bellows. The shape of the valve opening formed at the first valve plate may be one of a circle, a rectangle, a triangle, and an ellipse.